Generally, ordinary pitch has an amorphous structure. When this pitch is heated to temperatures of about 350.degree. C. to 550.degree. C. in an inert gas atmosphere, the molecules of the pitch undergo a thermal polycondensation reaction and become oriented to give rise to a kind of optically isomeric liquid crystal within the pitch. This liquid crystal is otherwise called a mesophase. The condition in which the mesophase occurs and grows can be observed with the aid of a polarizing microscope. The mesophase consists of pitch-forming aromatic molecules which have been oriented and associated together through their own interaction. The mesophase can be observed as anisotropic spherules under a polarizing microscope. A pitch of the type which contains such a mesophase is referred to as "crystalloidal pitch."
In recent years, it has been reported that shaped articles of carbon (graphite) having high density, high strength and isotropy can be produced by subjecting the crystalloidal pitch or mesophase, obtained by solvent extraction from the crystalloidal pitch in a powdered form, to compression molding and baking the compression molded articles. Since the crystalloidal pitch has heretofore been produced by heating and melting ordinary pitch in a container, the viscosity of the pitch is gradually increased during conversion with resulting nonuniformity of temperature distribution in the pitch. Thus the conversion of the pitch into a homogeneous crystalloidal pitch is difficult to attain by the prior art method. It is, therefore, impossible to consistently obtain a crystalloidal pitch with a constant mesophase content. To obtain a crystalloidal pitch having a high mesophase content, i.e., to obtain a mesophase of high purity, it has heretofore been customary to extract the mesophase fraction from the crystalloidal pitch containing same by use of a solvent such as quinoline or anthracene oil. This conventional process has the disadvantage that the raw pitch and the solvent must be used in large quantities and the solvent must be recovered after use.